Lecture 2: Basic principles (ecology and evolution) Flashcards
Parasite Ecology
ecology is the relationship between organisms and their abiotic and biotic environments.
for parasites, the host organism serves both as an ecological niche as well as an evolutionary environment.
- the parasite’s environment is primarily the host, but some stages do not require a host (such as eggs or juvenile forms)
Factors required for transmission of the parasite
- requires at least one host (or more!)
- the amount of parasites in the environment is related to the number of hosts in the environment
PARASITE NICHE
what is the ecological niche of the parasite?
- the specific part of the environment that they will thrive in.
- some parasites require more moist environments, others more dry, etc.
- the ecological niche can also be within the host body (specific area)
ex: malaria infects red blood cells
how do we assess the impact of parasitic diseases on human population?
- determine who is infected
- are infections distributed equally among all age groups and sexes?
- do some individuals have unusually high numbers of parasites?
macro vs micro-parasite
macroparasite:
- large parasites that don’t multiple in or on a host (like tapeworms, trematodes, nematodes)
- they can still be found in large numbers in/on host
microparasites:
-small parasites that multiply within a host
- ex: protozoan parasites
parasite populations
what knowledge about population structure is required to control infections?
we need to know:
- density (mean abundance)
- variance (shape of frequency distribution)
- a curve of best fit.
what factors (4) influence parasite populations?
Abiotic environmental factors: temperature, moisture, pollution
Biotic environmental factors: host density, intra-interspecific reservoirs, biotic sources of stress such as competitors and predators
Parasite characteristics: infectivity, virulence, dose, the competitiveness of parasite, co-evolutionary history
Host characteristics: innate and adaptive immunity, body conditions and reserves, age, behaviour, habitat preferences, skin microbiota.
parasite populations - multiple species infections
- a single host can be infected with several pathogens, including parasite species.
- parasite can interfere with one another in carious ways, especially in heavy intestinal infections
- this can also weaken the host.
PARASITE REPRODUCTION
- relationship between number of offspring and probability of individual success to survive:
- what are the two mechanisms we covered?
asexual reproduction
hermaphroditism
what is the difference in hermaphroditism between cestodes and trematodes?
- If you are infected with cestodes, you will always have one worm. You have ovaries and testies in EACH of the little spaces.
- If you are infected with trematodes, you are infected with one worm with the male and female and the whole worm has one male and female reproductive system.
What is Epidemiology (parasite epidemiology)?
- the study all all ecological aspects of a disease to explain its transmission, distribution, prevalence, and incidence in a population.
what can influence the distribution of parasites in a population?
HOST
- age
- sex
- social/economical status
- diet
- ecological conditions that favour completion of parasite life cycle
VECTORS
- snails, blood sucking arthropods, etc.
What is Parasite Landscape Epidemiology?
examples we discussed:
Factors playing a role in transmission include:
- If you have a parasite that can infect you while in the water, if you wash your clothing in the water (in less developed countries), you can have parasites that infect you by piercing your skin. - Cow poop contains parasite in their feces. The eggs that are in the feces of the cows can get into the river if the river floods into the grass field where the cow farm is. ○ The river will get infected with parasites. - Stagnant water which attracts mosquitos to lay their eggs. ○ Mosquitos are a carrier of many different parasites ○ If you cant control mosquito population, you cant control the spread of parasitic infections.
Parasite Evolution?
Evolutionary association between parasite and host.
The parasite may share a long evolutionary history by undergoing evolutionary change together, or the host and parasite are associated because the parasite has colonized the host and can no longer escape.
fitness of host/ parasite can play a role.
parasite evolution- the evolution of virulence
what is the advantage of being virulent vs benign?
som parasites seem to be especially virulent while others are relatively benign.
- parasites should evolve into less virulent forms, mainly because the death of the host should have a negative effect on parasite survival.
- balance between optimal virulence that maximizes parasite numbers and does not kill the host.
